Heparan N-Sulfatase (HNS) is a lysosomal enzyme involved in the degradation of heparan sulfate. A genetic defect resulting in the deficiency of this enzyme is known as mucopolysaccharidosis type IIIA or Sanfilippo disease type A. This rare autosomal recessive disease occurs in 1 of 24,000 live births, with no approved medical treatment available. Enzyme Replacement Therapy (ERT), is currently being clinically evaluated in which the recombinant form of the exogenous enzyme is introduced into a subject, to remedy an enzyme deficiency resulting from genetic mutation. In particular, recombinant HNS enzyme may be introduced into a patient diagnosed with Sanfilippo disease type A, to facilitate the degradation and biological turn-over of heparan sulfate. For the treatment, recombinant HNS glycoprotein is typically produced using a cell based expression system. Typically, the recombinant enzyme is a 54.7 kDa glycoprotein containing 5 potential N-glycosylation sites, along with several additional sites for post-translation modification. Some of these modification structures, such as those bearing terminal mannose-6-phosphate, are important for bio-efficacy while others may have roles in protein stability and/or solubility. As such, the diversity of different glycoforms present in the final recombinant product, which is influenced by both the upstream cell culture and downstream purification processes, can greatly impact the potential efficacy, pharmacodynamic and pharmacokinetic parameters of the therapeutic enzyme.
The production of recombinant protein therapeutics in a commercial setting thus typically requires control of the manufacturing processes which involves a battery of sensitive analytical methodologies to elucidate the physiochemical properties and monitor the purity, stability, and/or activity of the products. The ability to detect subtle physiochemical differences between purified batches is important towards achieving a controlled, reliable production process as well as a consistent, safe and efficacious product.